1. Technical Field
This disclosure relates generally to nacelles and engine build-up (EBU) hardware for aircraft propulsion engines, and more particularly, to the integration of cabin air pre-coolers into the same.
2. Background Information
A propulsion system for modern commercial transportation aircraft typically includes two or more turbofan engines. Each of these turbofan engines may be configured to deliver pressurized air from the engine's compressor section into the aircraft's cabin for use as environmental air. Such environmental air may be cooled after it is bled from the compressor section with a precooler to moderate its temperature. The precooler may be configured as a cross-flow heat exchanger, with cooling air ingested through the precooler to cool the environmental air.
The cooling air for the pre-cooler may be taken from any ambient air source, such as outside the nacelle or from the ambient air in the bypass air duct. The precooler may be mounted in the core compartment formed around the engine core and defined by the thrust reverser and/or other nacelle components. After the cooling air has passed through the precooler, it may be exhausted either into a duct that empties into the bypass fan duct or another ambient air region outside the nacelle, or it may be exhausted into the core compartment. The core compartment is ventilated with its own cooling air intakes and an exhaust that is positioned at the aft end of the core compartment between the bypass air exhaust and the engine exhaust. If spent cooling air is exhausted from the precooler into the core compartment, it flows through the core compartment and out of the existing core compartment exhaust.
The cooling air inlet and exhaust for the precooler are sized appropriately for the anticipated air flow through the precooler to adequately cool the environmental air. However, the range of the volume of cooling air flow can vary widely under certain conditions. If one of the engines or engine systems on the aircraft is disabled and not functioning, all of the environmental air for the cabin must be provided by the remaining engine and cooled in its associated precooler. In such a scenario of increased environmental air flow through the precooler, a corresponding increase in cooling air flow is also needed. This increased cooling air flow requirement must be accounted for in designing the cooling air inlet and exhaust system.